1. Technical Field
The present invention relates in general to a motor vehicle exhaust system. More particularly, the present invention relates to a catalytic exhaust treatment in a motor vehicle. More specifically, but without restriction to the particular embodiment and/or use which is shown and described for purposes of illustration, the present invention relates to an exhaust system having a series of catalytic converters disposed near the exhaust port of an internal combustion engine.
2. Discussion
Many years ago, the exhaust systems of automobiles consisted entirely of a pipe that attached to the exhaust ports of the combustion chamber of an internal combustion engine via a manifold. The major function of the pipe was to allow a controlled path for the hot exhaust gases to flow away from the engine and passenger compartments of the vehicle. Subsequently, mufflers were added to the rearward portion of the exhaust pipe to muffle the pulsating sounds of the exhaust gases to an acceptable level. In the mid 1970""s, a typical exhaust system also included a catalytic converter to remove pollutants from the exhaust gases. At first, all catalytic converters were disposed a substantial distance downstream of the exhaust ports in order to more effectively control the temperature of the catalyst.
Traditional 3-way, Carbon Monoxide-Hydrocarbon-Nitric Oxide, catalysts that are used on automobiles may not operate effectively at low or very high temperatures. At low temperatures, the catalyst does not convert the three main pollutants to Carbon Dioxide, Water, Nitrogen, and Oxygen. In fact, the typical catalyst is wholly ineffective until the catalyst heats up. The time needed for the catalyst to heat up is directly proportional to the distance between the catalyst and the engine. This is due primarily to the amount of structure (pipe walls, etc.) that the exhaust gases come in contact with before the catalyst. These surfaces act as a thermal mass and, in effect, reduce the temperature of the exhaust gas it as it moves downstream. In a downstream position, a typical catalyst could take as much as two minutes to heat up to an effective operating temperature. Therefore, the majority of the pollutants that the engine produces in the first two minutes would pass through the catalyst and emitted to the atmosphere. Unfortunately, if a catalyst operates at a temperature above a defined maximum, the catalyst will tend to age faster or even melt, thereby making it necessary to change catalysts. Therefore, placing the catalyst in the downstream position, significantly away from the exhaust ports, was a necessity.
Automotive engineers saw the need to provide catalysts that could heat up quicker and many improvements followed over the years, such as low mass substrates and close coupled catalysts. The low mass substrates provided for minimal thermal loss caused by the catalyst, thereby decreasing the needed heat-up time. Close coupled catalysts are, by definition, doser to the engine, and consequently, closer to the heat source. The improvements made to catalyst systems over the years have allowed for the catalyst to be placed closer to the exhaust port without being in danger of over-heating the catalyst. Examples of close coupled systems are described in U.S. Pat. Nos. 5,351,483 and 4,151,717. Many other systems have been proposed to decrease heat up time for the catalyst system, such as adding a heating element to the catalyst. However, such a solution has not been effective compared to the close coupled catalyst when cost and performance are considered.
The desire to reduce heat up time for an automotive catalyst has created a need to provide unique placement and arrangements of catalysts that effectively promote conversion of pollutants, especially in the first few minutes of engine operation.
Accordingly, it is a principal objective of the present invention to provide an effective catalyst configuration and arrangement for a motor vehicle.
It is another objective of the present invention to provide a catalyst configuration that reduces the amount of pollutants that escape through the exhaust system.
It is yet another objective of the present invention to provide a catalyst configuration that can reduce the amount of time needed for catalyst light-off to occur, i.e. the time needed to heat the catalyst to an appropriate operating temperature.
It is a further objective of the present invention to provide a catalyst configuration that can be packaged effectively in the engine compartment without affecting other components.
In one form, the present invention provides a catalyst configuration for a motor vehicle having an engine with a plurality of exhaust ports that carry exhaust gases from the combustion chamber of the engine. The exhaust gases leave the combustion chamber and flow in a downstream direction by first entering the exhaust ports. The exhaust gas from the exhaust ports then enters a plurality of tubes extending from a shell, the shell also includes an exit portion that decreases in diameter in the downstream direction. Each tube includes a conically shaped catalyst disposed adjacent to the exhaust port. The conically shaped catalysts have a front face and a rear face, said rear face being larger than said front face. The conically shaped catalysts also include cells that vary in size, the cell size increases in the downstream direction. The conically shaped catalysts are constructed from a metal substrate.
The shell encloses a main brick catalyst. The main catalyst is substantially cylindrical in shape and disposed downstream from the plurality of conically shaped catalysts. The main brick catalyst includes an angled front face and a conical downstream end. The downstream end has a conically shaped formation that decreases in diameter in the downstream direction at a rate greater than the rate at which the exit portion of the shell decreases in the downstream direction. The main catalyst brick is preferably constructed of a ceramic substrate. An exhaust pipe is attached to the exit portion of the shell and extends substantially to the rear of the vehicle.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.